In recent years, user terminals having both a cellular communication function and a wireless local area network (WLAN) communication function have been spread. Further, WLAN access points managed by an operator of a cellular communication network are increasingly used. In this regard, a technique of enhancing interworking of a cellular radio access network (RAN) and a WLAN is under review in 3rd Generation Partnership Project (3GPP).
For example, it is possible to reduce a traffic load of the cellular RAN by transferring traffic (data) transmitted and received by the user terminal from the cellular RAN to the wireless LAN (off load). Further, a network selection scheme for selecting an access network of accommodating traffic of the user terminal from the cellular RAN and the wireless LAN has been proposed (see Non-Patent Literature 1).